CO2 Acidizing Treatment of a Deepwater Subsea Well without Intervention

Abstract

Abstract An openhole gravel pack completion was performed in the vertical section of a high-permeability, oil formation in a deepwater subsea well. The open hole section was drilled with a synthetic oil-based drill-in fluid and completed with a circulating gravel pack using weighted brine. Initial production was satisfactory at over 10,000 BOPD. However, 11 months later, after a constant decline in production. the well was producing at an unacceptable rate of 3000 BOPD. Analysis of the formation mineralogy from an offset well in the same formation indicated a strong tendency for fines migration. In addition, there was concern that filter cake from the synthetic drill-in fluid could still be in place and would provide some restriction to optimum production rate. A HF sandstone acidizing treatment incorporating a CO2 preflush process for matrix oil well stimulation was recommended. Since the well was a deepwater subsea completion, a rig intervention on this well would have been extremely expensive. Therefore, the possibility of performing the matrix CO2 treatment through the flow line from the TLP floating production facility was reviewed and determined to be feasible. Procedures incorporating the use of the permanent downhole pressure gauges for rate and pressure control resulted in the restoration of a sustained production rate of 7000 BOPD. The procedure and steps utilized in the determination and execution of the final treatment design will be presented. Introduction The Morpeth Deepwater Development Project is located in 1,700 ft of water in the Gulf of Mexico. It consists of three (3) subsea oil production wells and one (1) subsea, seawater injection well for pressure maintenance. The wells flow back to the mini-TLP via individual flexible flowlines. The subsea production system and field layout are shown in Figure 1.